This invention relates to the field of truss joists typically constructed with wood top and bottom chords, connected by a series of diagonal horizontally spaced metal web members. These truss joists are used in the construction of buildings to provide support for the placement of floors or roofs. The invention specifically relates to the connection of the truss joist to the supporting walls or horizontal members.
In the construction of homes and buildings of various types and sizes, there is a need and demand for support members constructed of relatively lightweight material to support fairly large loads. The construction of various truss joist configurations fulfills this need through the use of relatively light wood chord members connected by the use of small structural web members typically fabricated of some type of metallic material.
A problem area of continued concern has been the means by which the ends of the truss joist are connected to the supporting walls or horizontal members, since the chord members of the truss joist are typically wood and the strength of these chord members is not sufficient to withstand the considerable shear and moment forces which result from various loads placed upon the truss member. To partially solve this problem prior art devices have placed the ends of the top chord member of the truss joist on the top surface of the support with the first pin connection to the first web member located directly above the top surface of the supporting wall. The placement of the pin connection to this first web member directly above the wall support and the connection of the wood chord member to this supporting wall alleviates the problem of shear and moment forces in wood because the shear forces are transmitted from the web member to the metal support connection and then to the top surface of the supporting wall.
However, as a result of placing the top chord member directly on the support surface with the pin connection directly above the support surface it is often necessary to place a notch or groove in the upper area of the support to accommodate the web member which angles up toward the pin connection from the bottom chord member to a point above the support surface located on top of the support. Placing a notch in the supporting wall for each truss joist is very time consuming and expensive in the construction of the building. An additional problem caused by the placement of the top chord member directly above the support surface is apparent in the construction of a floor or roof where there is the need to place filler blocks between the top chord members of adjacent truss joists along the upper surface of the support in order to fill in the gaps produced by the adjacent chord members.
Some prior art has attempted to alleviate this notch problem resulting from the differential between the planes of the upper surface of the chord member and the upper surface of the supporting wall by the utilization of a bracket on the end of the top chord member. The use of this bracket allows the first pin connection to be placed in spaced relation from the supporting wall, so that the requirement of placing a notch in the supporting wall or beam for the web member is eliminated. However, the actual differential between the planes remains along with the requirement for filler blocks, because the top chord is still placed above the supporting wall. It has been determined that, if the top chord is attached in some manner to the supporting wall so that the upper surfaces of the chord and the supporting wall are in the same plane, significant shear forces exist in the area of the chord adjacent the supporting wall and the first pin connections while significant moment forces exist between the first and second pin connections to a web member. The shear and bending moment diagrams for a typical truss joist are disclosed herein, reflecting the significant shear and moment forces, and the typical wood chord does not have the strength to withstand these forces. Consequently, the prior art has not been satisfactory in the practical solution of the problem, because the wood chord members do not have adequate strength to withstand the existing shear and bending moment forces when the truss joist is connected to the supporting wall in such a manner that the upper surface of the supporting wall is in the same horizontal plane as the upper surface of the chord member.
In prior art truss joist configurations the connection between the web members and the chord members requires the making of a vertical open channel within each of the chord members for receipt of the ends of the web members in order that, when the end of the web member is placed in the channel, a horizontal pin passing through the chord member will connect the web member to the chord. The introduction of a vertical open channel or groove into the chord member with a horizontal pin hole through the chord member at each web connection may have the disadvantage of weakening the chord member.